1. Field of the Invention
The present invention relates to an image capturing apparatus, and more particularly, to a technique of removing foreign substances such as dust attached to an optical member provided on a photographing optical axis.
2. Description of the Related Art
In an image capturing apparatus such as a digital camera which performs image sensing by converting an image signal into an electric signal, a light beam is received with an image sensor such as a CCD or a CMOS, then a photoelectric-converted electric signal, output from the image sensor, is converted into image data, and stored on a storage medium such as a memory card. In this image capturing apparatus, an optical low-pass filter, an infrared filter or the like is provided on the object side of the image sensor. When a foreign substance such as dust is attached to the cover glass of the image sensor and/or the surface of the filter, the shadow of the substance appears as a black spot in an obtained image, which degrades the quality of the image.
Particularly, in a lens-interchangeable single lens reflex digital camera, mechanical units such as a shutter and a quick return mirror are provided around the image sensor, and foreign substances such as dust from these mechanical units may be attached to the image sensor, the low-pass filter and the like. Further, upon lens exchange, dust and the like may enter from an opening of a lens mount into the camera main body, and may be attached to the image sensor, the low-pass filter and the like.
Japanese Patent Application Laid-Open No. 2003-319222 discloses a camera in which a dustproof curtain to pass a light beam is provided on the object side of the image sensor, and foreign substances attached to the surface of the dustproof curtain are removed by vibrating the dustproof curtain with a piezoelectric element.
According to the above conventional technique, to remove foreign substance attached to the surface of the dustproof curtain, a voltage is applied to the piezoelectric element connected to the dustproof curtain to drive the piezoelectric element, and the dustproof curtain is displaced in an optical axis direction, thus causing curtain vibration. However, as this technique causes curtain vibration by displacing the dustproof curtain in the optical axis direction, a vibration mode becomes complicated and vibration efficiency is lowered when the dustproof curtain has a shape other than a round shape.
Generally, the effective image sensing range of an image capturing apparatus has a rectangular shape with an aspect ratio of 4:3, 3:2 or the like. The effective light beam necessary for image sensing also has a rectangular shape. Accordingly, the round-shaped dustproof curtain has a large size with respect to the effective light beam in order to appropriately pass the light beam having the rectangular shape. It is disadvantageous in terms of convenience of layout to have such round dustproof curtain inside the image capturing apparatus, and such an inefficient layout causes an increase in the size of the image capturing apparatus.
Further, according to the above conventional technique, in addition to the inconvenience of layout, disadvantages in terms of production cost, optical function and optical performance are also created, as the necessity of the special member, the dustproof curtain, on the optical axis increases the number of parts, reduces the light beam transmissivity, and the like. Further, as high electric power is required to vibrate the dustproof curtain which is large with respect to the effective light beam, battery consumption is increased by the foreign substance removal operation.